Openzeppelin-contracts: Stop using syncronous HTTP requests

[LogvinovLeon]

🎉 Description

• [x] 🐛 This is a bug report.
• [x] 📈 This is a feature request.

It's kinda both.

📝 Details

Syncronous HTTP requests are deprecated in upcoming web3 version and provider-engine doesn't support them.
We use them in tests extensively, but it's mostly web3.eth.getBalance.
Let's remove them and be future-proof!

[arku]

@LogvinovLeon I'm on it!

[frangio]

I would love to move to async code but the problem is web3.js 0.x uses callbacks instead of promises. I wouldn't want the tests to be ridden with callbacks so we would have to promisify it somehow. @arun1595 keep that in mind!

[LogvinovLeon]

https://www.npmjs.com/package/es6-promisify

[arku]

@LogvinovLeon I've promisified the synchronous web3.eth.getBalance calls in the tests. Take a look at my PR when you get a chance.

Thanks!